2016 SAM goes mostly Positive bar the odd temporary wild swing late Autumn and Winter and early Spring then comes in October and goes negative rest of Spring and through Summer til March before going back to Positive again.

2017 SAM generally positive most of Autumn and Winter bar a one or two weeks where it went negative.. It continued to be positive into September... Then we enter October and this?

Surely not the same pattern as last yr? Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months? Love to know what is going on here.

Does anyone have any thoughts on this? Anyone?? Or we to busy arguing about other stuff to see what other posters post in here?

Ok :The SAM – as in the one measured by normalised (averaged) SLP differences between 40 and 65 degrees South of the Equator – I think would be largely governed by the extent to which tropical plumes [via the 576-thickness contour] impinge on the Sub-Tropical Ridge (STR) (at middle-to-high levels of the troposphere). One may notice on any publicly available model the extent to which the 576-to-540-thickness contour-range follows (waves around on) the isobars of the STR. Generally (as far as I can tell), the further north the SAM SLP differences influence, the less impinging the 576-thickness contour does, and the cooler and shallower the troposphere. As the 576 encroaches more [south], the difference between a deeper (warmer) and shallower (cooler) troposphere increases, and moisture, when it moves, encounters rougher (steeper) temperature and wind gradients, hence more variable MSLP and precipitation .

That is how I'm describing what I'm observing. If someone can interpret the above into SAM, ENSO IOD, PDO,... great!

Edited by Seira (13/10/201722:46)

_________________________
Silence can be beautiful because it is an avenue to peace of mind.

2016 SAM goes mostly Positive bar the odd temporary wild swing late Autumn and Winter and early Spring then comes in October and goes negative rest of Spring and through Summer til March before going back to Positive again.

2017 SAM generally positive most of Autumn and Winter bar a one or two weeks where it went negative.. It continued to be positive into September... Then we enter October and this?

Surely not the same pattern as last yr? Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months? Love to know what is going on here.

Does anyone have any thoughts on this? Anyone?? Or we to busy arguing about other stuff to see what other posters post in here?

Ok :The SAM – as in the one measured by normalised (averaged) SLP differences between 40 and 65 degrees South of the Equator – I think would be largely governed by the extent to which tropical plumes [via the 576-thickness contour] impinge on the Sub-Tropical Ridge (STR) (at middle-to-high levels of the troposphere). One may notice on any publicly available model the extent to which the 576-to-540-thickness contour-range follows (waves around on) the isobars of the STR. Generally (as far as I can tell), the further north the SAM SLP differences influence, the less impinging the 576-thickness contour does, and the cooler and shallower the troposphere. As the 576 encroaches more [south], the difference between a deeper (warmer) and shallower (cooler) troposphere increases, and moisture, when it moves, encounters rougher (steeper) temperature and wind gradients, hence more variable MSLP and precipitation .

That is how I'm describing what I'm observing. If someone can interpret the above into SAM, ENSO IOD, PDO,... great!

SAM = P*40°S – P*65°S

Normalised monthly zonal pressure differences.

Does have shortcomings like many of its fellow indices and models.

If the pressure at either latitude alters nonsynchronously with the other the index alters - positive means relatively higher value of P*65South in relation to P*40South and negative vice versa - pardon if this is already known to the reader.

I think the normalised bit in the above, takes out the component of variability due to seasonallity.

The original question- ”Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months?” may be a bit of a red herring - cooler and/or warmer months where exactly? may be more relevant.

If the pressure at either latitude alters nonsynchronously with the other the index alters - positive means relatively higher value of P*65South in relation to P*40South and negative vice versa - pardon if this is already known to the reader.

I think the normalised bit in the above, takes out the component of variability due to seasonallity.

The original question- ”Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months?” may be a bit of a red herring - cooler and/or warmer months where exactly? may be more relevant.

The above may be misleading. I've found a couple of sources which appear to be contradictory. Will post once resolved.

Mike ,The NW Pacific is fast approaching or maybe even past it’s significant influence in the feedbacks on the Atmosphere . So we are going to see the Sth Hem / Western Pacific ( which is more of a reference to Indonesia and Austral waters .

So I can’t see that NW region driving too many feedbacks in the coming weeks .

As for the SAM , I believe that the Nodal LWT will be deflected in part by the ENSO setup in Eastern Australlia . The SAM and the frontal progressions will most likely concentrate where the Tropical SST’s are more conclusive to where their will be less longitude life blocking . Atleast in repitiveness . The ACPW should effect this and to some extent it looks okay going forward . The dynamic mixing will make it harder to predict what classical setups may deliver in the way of Frontal progressions , aligned troughs and water vapour infeeds . As for the Antarctic sea ice hole , if 1974-75 is anything to go by it says that if the whole is water current driven and not some unknown upper atmospheric deficiency . Then we are in for a radical ride . Lastly the waters Sth of the Equator in the Far East will have fast warming as the now continual pattern of suppressed OLR will result in that warming fast in the coming months . More importantly is the constant conveyor of more sub surface driven gyre and the actual Sth Pacific gyre continually pushing this warming water west . As for down here , violent transitions between cool , warm , wet and dry should be the order of the day for the next two months . Regardless of ENSO’s resultant ( which to me is still clear ) , the summer should be cooler .

Mike ,The NW Pacific is fast approaching or maybe even past it’s significant influence in the feedbacks on the Atmosphere . So we are going to see the Sth Hem / Western Pacific ( which is more of a reference to Indonesia and Austral waters .

Not sure why you think this. We are maybe two months away from SH tropical convection season firing up and taking the focus of tropical convection into the southern hemisphere. If anything we are entering a period where the NW Pacific is more important because tropical convection is more likely to be closer to the equator where it can have a strong influence, and less likely to be far north near Japan having no influence.

It shows the weakening of the polar vortex, as normally happens at this time of year.The chart shows the temperature at the heights of 10hPa.This JMA dataset shows a 'SSW' over September and the last couple of weeks showing a period of stable temperatures.

If the pressure at either latitude alters nonsynchronously with the other the index alters - positive means relatively higher value of P*65South in relation to P*40South and negative vice versa - pardon if this is already known to the reader.

I think the normalised bit in the above, takes out the component of variability due to seasonallity.

The original question- ”Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months?” may be a bit of a red herring - cooler and/or warmer months where exactly? may be more relevant.

The above may be misleading. I've found a couple of sources which appear to be contradictory. Will post once resolved.

2. The Southern Annular Mode (SAM) is the principal mode of variability in the Southern Hemisphere (SH) extra-tropics, describing ~30% of SH climate variability. Its spatial structure comprises synchronous pressure anomalies of opposite sign in mid and high latitudes: when pressures are anomalously high over Antarctica the SAM is defined as being in its positive phase and vice versa

I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.

I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.

Bold - That may have to do with topography, and the difference in land area in the north.

I agree that without the stability of the temperature in the 10-hPa vicinity, things could be very different too.

Edited by Seira (15/10/201722:31)

_________________________
Silence can be beautiful because it is an avenue to peace of mind.

I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.

There's a distinction made between major and minor warmings - we do get the latter though I'm not sure of frequency - has to involve a rise of at least 25c in temp in a week or less(this year would have gotten over that threshold I think?) - doesn't has to involve a reversal of westerlies on the stratospheric southern polar vortex perimeter(which is the case with major warming).

I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.

Bold - That may have to do with topography, and the difference in land area in the north.

I agree that without the stability of the temperature in the 10-hPa vicinity, things could be very different too.

I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.

There's a distinction made between major and minor warmings - we do get the latter though I'm not sure of frequency - has to involve a rise of at least 25c in temp in a week or less(this year would have gotten over that threshold I think?) - doesn't has to involve a reversal of westerlies on the stratospheric southern polar vortex perimeter(which is the case with major warming).